Our Local Group of galaxies is dominated by M31, the Andromeda Galaxy. Our Milky Way is the second banana in this bunch. M31 is, not surprisingly, located in the constellation Andromeda. It is a mere 2.54 Mly away, a spiral galaxy 220 kly in diameter, composed of about 1 trillion stars. By comparison our galaxy is about 170 kly in diameter with upwards of 400 billion stars. (Ref: Wikipedia and J. Kanipe and D. Webb, Annals of the Deep Sky, vol. 1)

It is blue shifted with z = -0.001001, hurtling towards us at about 110 km/s (68 miles/s). Its tangential velocity is much smaller, and so M31 is expected to collide with us in about 4 billion years. (This future event used to worry me to no end when I first learned about it as a child. But then I learned that the earth would probably be burnt to a crisp by then anyway by an aging, bloated sun, so my worries were shifted back to our own solar system.) The likely scenario is that the two galaxies will mostly pass through each with very little chance of actual star collisions given the stars' vast distances from one another. However, the gravity dance will be quite complex and distort both spirals heavily. It is likely that they will eventually merge into an elliptical galaxy with no visible memory of their once distinct spiral arms. Here's a short video about the impending collision if you are interested.

Also present in the image are M31's satellites. There are 14 known dwarf galaxies around Andromeda. The two most prominent here are M32 and M110. M32 lies in front of the disk just below the core in my image. M110 is the larger one to the upper right from the core. Both are interacting with Andromeda, and there is a faint dust lane connecting M110 to M31 that can be seen in my image if you look carefully. In this stream are metal-rich stars that have been stripped away from the satellite galaxy.

There don't appear to be any notable foreground Milky Way stars in this image (to my knowledge) with the exception of one with a known expolanet planetary system. It is located in the upper right corner, and I have labeled it on the annotated image. The designation is HAT-P-16. The star's mass is 1.218, radius 1.237 multiples of the sun. The expolanet listed is 4.19 times the mass and 1.3 times the radius of Jupiter. It revolves around its star in 2.78 days (!) at a distance of only 0.0413 AU (!). It was discovered in 2010 using the primary transit method. (Ref: Stellarium)

There are many background PGC galaxies in the annotated image. The ones that caught my attention due to their having a more discernible shape are PGC2171339 (left middle edge of frame) and PGC2314 (upper right from M110). Several of the others looks have shapes that look slightly better than smudges on my image, but I'll focus on these two. The first is listed my SIMBAD as LEDA 2171339, but nobody seems to have further data on it. I would guess it's an edge-on spiral, maybe a distant Sombrero Galaxy with an edge-on dark rim, but frankly that's hard to guess with just a few pixels available. The second is listed by SIMBAD as UGC 394, and according to NED has redshift z=0.0187 with radial velocity around 5500 km/s, distance about 79 Mpc. Its morphology is a barred spiral if I understand the codes. You couldn't have guessed that from my tiny image, but now that I know it, sure, it looks like a barred spiral to me!

This is an LRGB image. I decided to bin the color frames on this occasion. I also increased the magnitude of the dithering in order to try to smooth out the background better, however I noticed that my first LRGB construction still came out with some nonuniform shading that I was able to better remove in a second pass.

In PixInsight I used the PhotometricColorCalibration process to calibrate the colors. The color scheme setting that I used was for balancing out G2V stars. M31 is naturally rather anemic in coloring in my opinion, and my combination followed suit. I like spiral galaxy images with pretty blue arms and yellowish core from an aesthetic point of view, but my choice of using PCC with G2V setting didn't support that. Following that I tried not to saturate the colors too much.

I ended up reducing the number of color frames to just an hour each in RGB in order to select out the best SNR frames. This seemed to do a better job in smoothing out the background.

For the L frame I settled on 180s exposure frames as going higher saturated even more of M31's core, although upon finishing the processing I think the core still got too saturated and lacks any detail. I will remember that in the future when I return to M31 once again. I will go for yet shorter exposure.

Still, I am pleased with how it turned out with the caveats listed above. I hope you enjoy.

Any comments and suggested would be greatly appreciated.